Reference and current Trophic Level Index of New Zealand lakes_MS&SuppInfo_2020.pdf
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Abell, J. M., van Dam-Bates, P., Özkundakci, D., & Hamilton, D. P. (2020). Reference and current Trophic Level Index of New Zealand lakes: benchmarks to inform lake management and assessment. New Zealand Journal of Marine and Freshwater Research, 54(4), 636–657. https://doi.org/10.1080/00288330.2020.1726974
Permanent Research Commons link: https://hdl.handle.net/10289/13734
Knowledge of trophic status is fundamental to understanding the condition and function of lake ecosystems. We developed regression models to predict chlorophyll a concentrations (chl a) in New Zealand lakes for reference and current states, based on an existing dataset of total nitrogen (TN) and total phosphorus (TP) concentrations for 1031 lakes. Models were then developed to predict Secchi depth based on chl a and a sediment resuspension term applicable to shallow lakes. Estimates of all four Trophic Level Index (TLI) variables (chl a, TN, TP and Secchi depth) were analysed to estimate reference and current state TLI for the nationally representative sample of 1031 lakes. There was a trend of eutrophication between reference and current states, with systematic differences among lake geomorphic types. Mean chl a increased 3.5-fold (2.42 mg m¯³ vs. 8.32 mg m¯³) and mean Secchi depth decreased (indicating lower clarity) by approximately one-third (9.62 m vs. 6.48 m) between reference and current states. On average, TLI increased by 0.67, with the TLI increase >1 in approximately one-third (31%) of lakes. This study informs the status of lake ecosystems in NZ and provides benchmarks to guide management and assessment.
Taylor & Francis
This is an author's accepted version of an article published in New Zealand Journal of Marine and Freshwater Research. © 2020 The Royal Society of New Zealand.